Fluke 8842a instruction manual Evaluating Static Signals, Device REF. DES

8842A

Instruction Manual

Table 6-20. Analog Control Devices

DEVICE

REF. DES.

Relay Buffer

Quad Comparator

Quad Analog Switch

Quad Analog Switch

Quad Analog Switch

Quad Analog Switch

Quad Analog Switch

8-Bit Latch

Quad Analog Switch

Quad Analog Switch

* Option -09 only

U201

U305

U301

U302

U303

U402

U403

U803 *

U804 *

U808 *

Correct operation of 8-bit latch U803, situated on the True RMS AC PCA (Option -09 only), can be determined directly since all of its inputs and outputs are available. Again, outputs of quad analog switches U804 and U808 are not available and must be determined by analog means.

6-60. Evaluating Static Signals

Table 6-21 may be used to determine whether or not proper signals are reaching any particular analog control device. It may also be used to quickly exercise all of the devices before beginning analog troubleshooting if it is still unclear as to which devices are suspect. A number of the inputs to these devices are static which makes them particularly easy to check.

For example, suppose quad comparator U305 appears not to be working. Connect a scope to U305-11 and step the 8842A through all functions and ranges in the following sequence:

1.VDC: 20 mV, 200 mV, 2V, 20V, 200V, 1000V

2.VAC: 200 mV, 2V, 20V, 200V, 700V

3.2 WIRE kΩ: 200Ω, 2k, 20k, 200k, 2M, 20M

4.4 WIRE kΩ: 20Ω, 200Ω, 2k, 20k, 200k, 2M, 20M

5.mA DC: 200 mA, 2000 mA

6.mA AC (one range only)

While doing this, observe the state of U305-11. As shown in Table 6-21, this 24-range sequence will produce the following pattern at U305-11:

111010 00000 111100 1111100 000

6-52